What was found
CREW REPORTED RIGHT AND LEFT REVERSER UNSAFE AMBER MESSAGE ON TAKEOFF. CREW RETURNED TO FIELD AND LANDED WITHOUT INCIDENT. MESSAGE OCCURRED TWO (2) TIMES ON LANDING WITH REVERSER NOT ARMED. MAINTENANCE TROUBLESHOT USING AIRCRAFT FIM (FAULT ISOLATION MANUAL). FUNCTION CHECK GOOD. PERFORMED OPERATIONAL CHECK ON LEFT AND RIGHT THRUST REVERSER SYSTEM. OPERATIONAL CHECK GOOD. PERFORMED NUMEROUS GROUND RUNS AND DEPLOYED / STOWED RIGHT AND LEFT THRUST REVERSERS WITH NO ASSOCIATED FAULTS OR MESSAGES. INTERROGATED PSEU (PROXIMITY SENSOR ELECTRONIC UNIT) FOR FAULTS AND FOUND NO ERRORS PRESENT IN MEMORY. COULD NOT DUPLICATE DISCREPANCY ON GROUND. AIRCRAFT RELEASED FOR SERVICE. CHECKS PERFORMED BY MAINTENANCE WERE ACCOMPLISHED USING AIRCRAFT MAINTENANCE MANUALS.